1. Field of the Invention
The present invention relates to a compound circuit board and related radar device, and more particularly, to a compound circuit board with small thickness and related radar device.
2. Description of the Prior Art
An automotive radar system utilizes wireless signal transceivers disposed inside vehicle bumpers or grills to transmit or receive millimeter-wave wireless signals for ranging and information exchange applications. Since shock-absorbing Styrofoam or glass fibers are usually disposed inside the vehicle bumpers, the available space is limited, which therefore increases design difficulty for the wireless signal transceivers. In addition, if the automotive radar system is produced for sales of after-market, i.e. vendors for the radar systems do not participate in decision-making of materials and thickness of the bumpers, in such a condition, size requirements for the wireless signal transceivers become stricter in order to comply with different cars.
In general, a conventional wireless signal transceiver in an automotive radar system includes three major portions: digital signal processing (DSP), electronic control unit (EDU), and radio-frequency (RF), and each portion includes corresponding circuits and circuit boards. The DSP portion is mainly used for processing and controlling operations of the radar system; the RF portion includes elements such as a microwave antenna, a power amplifier, and a low noise amplifier, and works with a monolithic microwave integration circuit (MMIC) and related circuits to transmit and receive wireless signals; and the ECU portion is used to transmit safety-aided information to the users via a human-machine interface. In order to realize the three portions mentioned above, a conventional microwave automotive radar system needs to include a DSP board, an ECU board, and an RF antenna board accordingly. The substrates of the DSP board and the ECU board are made of FR4 material, and the RF antenna board requires a low dielectric constant and low loss substrate. Different boards are connected by a board-to-board connector so that the microwave automotive radar system may accurately detect relative distance, velocity, and angle of an object and generate warning signals to the users. In such a situation, even though the thickness of a circuit board is generally less than 2 mm, the volume or the thickness of the end-product often increases significantly (e.g., larger than 10 mm in general) after adding the connectors.
Due to the limited space for disposing the automotive radar product, it is a common goal in the industry to effectively reduce the volume or the total thickness of the automotive radar product.